1. Field of the Invention
The present invention relates to a radio communication device and a mobile communication system and, in particular, to a radio communication device and a mobile communication system which employ a CDMA (code division multiple access) system using spreading codes.
2. Description of the Rerated Art
In a CDMA mobile communication system, a large number of mobile stations are divided into a plurality of groups for avoiding concentration of call requests from the mobile stations to a base station. The base station transmits access right allocating information to the mobile stations using a control channel such as a paging channel or a broadcasting channel. The access right allocating information represents an access right allocated to each of the groups for call requests from the mobile stations belonging to the corresponding group.
The mobile stations carry out, for example, calling for location registrations on the basis of the access right allocating information.
In the CDMA mobile communication system, regardless of whether the control channel for transmitting the foregoing access right allocating information is a paging channel or a broadcasting channel, the access right allocating information is subjected to error correction coding along with other channel information for countermeasure against bit errors caused due to noise, then spread by a spreading code and multiplexed with the other channel information so as to be transmitted to the mobile stations as a multiplex spread signal.
Thus, for knowing whether an access right is allocated, each mobile station re-spreads or despreads the received multiplex spread signal using the foregoing spreading code and then applies error correction decoding to the despread signal with respect to each of frames of the channel information including the access right allocating information.
Accordingly, in the conventional CDMA mobile communication system, the error correction decoding is essential at each of the mobile stations with respect to each of the frames of the channel information including the access right allocating information so that it takes a relatively long time for confirming whether the access right is allocated or not. Thus, delays are caused in the confirmation processes for the access rights at the respective mobile stations so that concentration of call requests is liable to occur.
For avoiding such call request concentration so as to smoothly deal with call requests from as many mobile stations as possible, it is quite effective to shorten the time required for the confirmation process for the access right allocation.